Large Power Factors in Wide Band Gap Semiconducting RFeO₃ Materials for High-Temperature Thermoelectric Applications

Abstract

While most of the thermoelectric materials work well only at low and mid temperatures, high-temperature thermoelectric materials (T > 900 K) are equally important for the operation of deep-spacecraft missions, nuclear reactors, and high-temperature industrial reactors. To accomplish this demand, this work provides insights into wide band gap semiconducting RFeO 3 (rare-earth orthoferrites) for high-temperature thermoelectric applications. Using the first-principles density functional theory calculations, we have demonstrated the coexistence of extremely flat and corrugated flat bands near the Fermi region in a wide band gap material. The presence of such features enhances and sustains the thermopower, electrical conductivity, and power factor, which are the crucial factors for the efficiency of thermoelectric materials. Semiclassical Boltzmann formalism was then employed to study the transport properties of four orthorhombic RFeO 3 materials (R = Pr, Nd, Sm, and Gd). Our results reveal high Seebeck coefficients (thermopower) along with the large electrical conductivities over the high hole doping carrier concentration and in the high-temperature region (T > 900 K). Furthermore, significantly large power factors are obtained with very low theoretical minimum lattice thermal conductivity in the range 1.41−1.51 W m −1 K −1 . These huge power factors directly suggest the maximum power output in RFeO 3 , which we believe is a more appropriate performance index than the figure of merit, especially for hightemperature thermoelectric applications. We also emphasize that the outcomes of our work would be certainly useful for experimentalists in designing high-temperature thermoelectric materials.

Ternary Ag2Se1–xTex: A Near-Room-Temperature Thermoelectric Material with a Potentially High Figure of Merit

“…It is worth noting that to maintain the simplicity of the used band model, E def used here is a phenomenological parameter which includes both the interaction of electrons–phonons and other potential energies of electron scattering mechanisms. In thermoelectric materials, various electron scattering mechanisms such as alloying scattering, boundary scattering, ionized impurity scattering, and acoustic/optical phonon scattering can affect the carrier transport. − The T -dependent μ W in our work (Figure a) indicates that the acoustic phonon scattering dominates the carrier transport with the possibly existing alloying scattering and boundary scattering with increasing Te content. It is challenging to decrease the interaction of electrons–phonons; therefore, we can focus on diminishing the structural defects to reduce the phenomenological E def in the future study.…”

Physical Insights on the Lattice Softening Driven Mid‐Temperature Range Thermoelectrics of Ti/Zr‐Inserted SnTe—An Outlook Beyond the Horizons of Conventional Phonon Scattering and Excavation of Heikes’ Equation for Estimating Carrier Properties

“…The phenomenon of coexistence of such flat and corrugated bands near E F contributing to the enhanced thermoelectric performance has not been reported so far for any of the SnTe‐based materials, thus providing an exciting prospect for future exploration in this direction (for SnTe thermoelectrics). In the past, the corrugated flat‐band driven improved power factor has, however, been reported for materials such as RFeO 3 (wide bandgap), where R = Pr, Nd, Sm, and Gd, [ 85 ] and PtSb 2 . [ 84 ]…”

Rare Earth Orthoferrite Tuning of Transmitted Waves as Natural Metamaterials

“…The reason was that after the temperature dropped, the resonances shifted from the frequency band where transmittance decreased to nearly zero, and the resistance became smaller. Thus, the transmittance decreased 64 and eventually dropped to nearly zero as the temperature was lowered very low. 65 Physically, there are three types of magnetic interactions in RFeO 3 : Fe 3+ −Fe 3+ , Fe 3+ −R 3+ , and R 3+ −R 3+ .…”